1. Field of the Invention
The present invention is related to an acoustic wave sensing device integrated with micro-channels, and more particularly to an acoustic wave sensing device that has a substrate made of a piezoelectric material and is processed by techniques of micromaching. The sensing device of the present invention can be used for analysis of specific ingredients of liquid or gas.
2. Description of Related Art
Due to the transmission characteristic of flexural plate waves (FPW) in liquid, i.e. the energy propagation of flexural plate waves is restricted in liquid, flexural plate waves are used for liquid sensors nowadays. Conventional FPW components are made substantially by using silicon as substrates, forming piezoelectric films on there, and finally performing an etching process on the same. However, in practical applications, it is difficult to control the characteristics of multi-layer films, and the characteristics of piezoelectric films are the important parameters that determine the performance of the FPW components. Furthermore, the structure of the piezoelectric films is fragile. Hence, the FPW components are easily broken.
In U.S. Pat. No. 5,212,988, a layer structure made of a piezoelectric material is proposed to produce symmetric or asymmetric Lamb waves. In this design, a ground electrode layer is needed. U.S. Pat. No. 5,212,988 shows another case of conventional FPW components, which are made by using film-depositing and silicon-etching processes. Furthermore, in U.S. Pat. No. 6,688,158, a sacrificial layer micromachining process is used to make components with small areas for formation of arrays, and the components are made of a piezoelectric material, such as aluminum nitride, zinc oxide, or lead zirconium titanate.
In the literature, in “Vapor recognition with an integrated array of polymer-coated flexural plate wave sensors,” Volume 62, pp. 121-130, in 2000, Qing-Yun Caiz et al propose a FPW structure, which has a silicon plate as substrate and a piezoelectric film as an actuator. This FPW structure can be designed to form an array structure combined with a measuring system. It is used mainly for recognition of gas.
In the literature, in “Microfabricated Lamb wave device based on PZT Sol-Gel thin film for mechanical transport of solid particles and liquids,” Journal of Microelectro-mechanical, Volume 73, pp. 112-123, in 2001, Philippe Luginbuhl et al. propose a FPW structure to illustrate the mechanical transport of solid particles and liquids caused by FPW. However, the sensing results obtained in fluids are not demonstrated.